SCC test through a transparent Al2O3 single crystal rod inserted into the observation port
of the autoclave. Size of the rod was 20 mm in diameter and 160 mm long. A gap between
the end of the rod and the specimen surface was 10 mm to avoid fluctuation of the
observed image due to the spatial distribution of solution density induced by thermal convection.
A high-performance charge-coupled device (CCD) camera system was employed
to observe and record the cracking images. The observation area of the CCD camera system
was about 4 mm · 5 mm when a 50· objective lens was used. In order to observe all
the cracks on the whole gauge area 4 mm wide and 10 mm long, the head part of the CCD
camera was mounted on an X–Y–Z stage which could move over the volume
20 mm · 20 mm · 20 mm. The stage and the recording system were operated synchronically
using a computer. It was confirmed that reasonably clear images of the crack initiation
and growth behavior could be obtained in the high temperature water up to 300 C.
Details of this apparatus are described elsewhere